Enter your R1, R2, and C1 values (with their units) into this 555 Timer Astable Calculator to find the output frequency of your oscillator circuit, plus the full timing breakdown — period (T), duty cycle, time high (T1), and time low (T0).
Frequency
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Period (T)
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Duty Cycle
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Time High (T1)
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Time Low (T0)
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In astable mode, the 555 timer produces a continuous square wave output that alternates between high and low states. In monostable mode, it produces a single output pulse when triggered. Astable mode is used for oscillators and clocks, while monostable is used for timing delays.
No, a standard 555 astable circuit cannot achieve exactly 50% duty cycle because the capacitor charges through both R1 and R2, but discharges only through R2. The duty cycle is always greater than 50%. To get 50% duty cycle, you need additional components like a diode.
Typical values are R1: 1kΩ to 100kΩ, R2: 1kΩ to 1MΩ, and C1: 10nF to 1000μF. The exact values depend on your desired frequency and duty cycle. For audio frequencies, use smaller capacitors (nF range) with moderate resistor values.
The frequency formula is f = 1.44 / [(R1 + 2×R2) × C1], where R1 and R2 are in ohms and C1 is in farads. This gives you the frequency in Hz. The period is simply 1/frequency.
The maximum reliable frequency for a standard 555 timer is typically around 500kHz to 1MHz, depending on the specific IC and circuit conditions. For higher frequencies, consider using specialized oscillator ICs or different timer configurations.
Real-world variations occur due to component tolerances (typically ±5% to ±20% for resistors and capacitors), temperature effects, and the 555 IC's internal voltage thresholds. Use precision components and consider temperature coefficients for critical applications.
The 555 timer operates from 4.5V to 15V DC supply. Common voltages are 5V, 9V, or 12V. The supply voltage affects the output voltage levels but doesn't significantly change the timing calculations, as they depend primarily on the RC time constants.